I FIND there is enough of the troglodyte in most persons to make them love the rocks and the caves and ledges that the air and the rains have carved out of them.

The rocks are not so close akin to us as the soil; they are one more remove from us; but they lie back of all, and are the final source of all. I do not suppose they attract us on this account, but on quite other grounds. Rocks do not recommend the land to the tiller of the soil, but they recommend it to those who reap a harvest of another sort the artist, the poet, the walker, the student and lover of all primitive open-air things.

Time, geologic time, looks out at us from the rocks as from no other objects in the landscape. Geologic time! How the striking of the great clock, whose hours are millions of years, reverberates out of the abyss of the past! Mountains fall, and the foundations of the earth shift, as it beats out the moments of terrestrial history. Rocks have literally come down to us from a fore world. The youth of the earth is in the soil and in the trees and verdure that springs from it; its age is in the rocks; in the great stone book of the geologic strata its history is written. Even if we do not know our geology, there is something in the face of a cliff and in the look of a granite boulder that gives us pause and draws us thitherward in our walk. We linger beneath the cliff, or muse and dream amid its ruins as amid the ruins of some earth temple; we pause beside the huge boulder, or rest upon it and survey the landscape from its coign of vantage; we lay our hand upon it as upon some curious relic from a world that we know not of. The elemental, the primordial, the silence of ages, the hush and repose of a measureless antiquity look out upon us from the face of the rocks. "The menacing might of the globe" is in the cliffs and the crags; its ease and contentment are in the slumbering boulders. One might have a worse fate than to have his lot cast in a rockless country a treeless country would be still worse: but how the emigrant from New England or New York to the prairie States or to the cotton States, must miss his paternal rocks and ledges! A prairie farm has no past, no history looks out of it, no battle of the elemental forces has been fought there, and only a very tame, bloodless battle of the human forces.

A landscape without rocks lacks something. Without the outcropping ledge, the faces of the hills lack eyebrows; without a drift boulder here and there, the fields lack the rugged elemental touch. Next to the trees, rocks are points of interest in the landscape. Slumbering here and there upon the turf, they enhance the sense of repose. How expressionless and uninteresting the landscape in one of the prairie States, or in one of the Southern States, contrasted with a New England or a New York farm! The grazing or ruminating cattle add a picturesque feature, but the gray granite boulders have been lying there chewing their stony cuds vastly longer. How meditative and contented they look, dreaming the centuries away!

The rocks have a history; gray and weather-worn, they are veterans of many battles; they have most of them marched in the ranks of vast stone brigades during the ice age; they have been torn from the hills, recruited from the mountain-tops, and marshaled on the plains and in the valleys; and now the elemental war is over, there they lie waging a gentle but incessant warfare with time, and slowly, oh, so slowly, yielding to its attacks! I say they lie there, but some of them are still in motion, creeping down the slopes, or out from the clay-banks, nudged and urged along by the frosts and the rains, and the sun. It is hard even for the rocks to keep still in this world of motion, but it takes the hour-hand of many years to mark their progress. What in my childhood we called "the old pennyroyal rock," because pennyroyal always grew beside it, has, in my time, crept out of the bank by the roadside three or four feet. When a rock, loosened from its ties in the hills, once becomes a wanderer, it is restless ever after, and stirs in its sleep. Heat and cold expand and contract it, and make it creep down an incline. Hitch your rock to a sunbeam, and come back in a hundred years, and see how much it has moved. I know a great platform of rock weighing hundreds of tons, and large enough to build a house upon, that has slid down the hill from the ledges above, and that is pushing a roll of turf before it as a boat pushes a wave, but stand there till you are gray, and you will see no motion; return in a century, and you will doubtless find that the great rock raft has progressed a few inches. What a sense of leisure such things give us hurrying mortals!

One of my favorite pastimes from boyhood up, when in my home country in the Catskills, has been to prowl about under the ledges of the dark gray shelving rocks that jut out from the sides of the hills and mountains, often forming a roof over one's head many feet in extent, and now and then sheltering a cool, sweet spring, and more often sheltering the exquisite moss-covered nest of the phœbe-bird. These ledges appealed to the wild and adventurous in the boy. The primitive cave-dweller in me, which is barely skin-deep in most boys, found something congenial there; the air smelled good; it seemed fresher and more primitive than the outside air; it was the breath of the rocks and of the everlasting hills; the home feeling which I had amid such scenes doubtless dated back to the time when our rude forebears were cave-dwellers in very earnest. The little niches and miniature recesses in the rocks at the side were so pretty and suggestive, and would have been so useful to a real troglodyte. Of a hot summer Sunday one found the coolness of the heart of the hills in these rocky cells, and in winter one found the air tempered by warmth from the same source. To get down on one's hands and knees and creep through an opening in the rocks where bears and Indians have doubtless crept, or to kindle a fire where one fancies prehistoric fires have burned, or to eat black birch and wintergreens, or a lunch of wild strawberries and bread where Indians had probably often supped on roots or game – what more welcome to a boy than that?

As a man I love still to loiter about these open doors of the hills, playing the geologist and the naturalist, or half-playing them, and half -dreaming in the spirit of my youthful days. Phœbe-birds' nests may be found any day under these rocks, but on one of my recent visits to them I found an unusual nest on the face of the rocks such I had never before seen. At the first glance, from its mossy exterior, I took it for a phœbe's nest, but close inspection showed it to be a mouse's nest – the most delicate and artistic bit of mouse architecture I ever saw – a regular mouse palace; dome-shaped, covered with long moss that grew where the water had issued from the rocks a few yards away, and set upon a little shelf as if it had grown there. There was a hole on one side that led to the soft and warm interior, but when my forefinger called, the tiny aristocrat was not in. Whether he or she belonged to the tribe of the white-footed mouse, or to that of the jumping mouse, I could not tell. Was the device of the mossy exterior learned from the phœbe? Of course not; both had been to the same great school of Dame Nature.

Through the eyes of the geologist I see what the agents of erosion have done, how the tooth of time has eaten out the layers of the soft old red sandstone, and left the harder layers of the superimposed Catskill rock to project unsupported many feet. I see these soft red layers running through under the mountains from valley to valley, level as a floor, and lending themselves to the formation of the beautiful waterfalls that are found here and there in the trout brooks of that region. At one such waterfall, a mile or more from the old schoolhouse, we used to go, when I was a boy, for our slate pencils, looking for the softer green streaks in the crumbling slaty sandstone, and trying them on our teeth to see whether or not they were likely to scratch our precious slates. In imagination I follow this slaty layer through under the mountains and see where it is cut into by other waterfalls that I know, ten, twenty, thirty miles away. At those falls the water usually makes a sheer leap the whole distance, – twenty, thirty, or fifty feet, as the case may be, – the harder rock at the top always holding out while the softer layers retreat beneath it, forming in this respect miniature Niagaras. When near one of these falls I seldom miss the opportunity to climb the side of the gorge under the overhanging rock and inspect its under surface, and feel it with my hand. The elements have here separated the leaves of the great stone book and one may read some of the history written there. When I pass my hand over the bottom side of the superincumbent rock, I know I am passing it over the contours, the little depressions and unevennesses of surface, of the mud of the old lake or inland sea bottom, upon which the material of the harder rock was laid down more than fifty millions of years ago. There are here and there little protuberances, the size of peas and beans, which probably mark where little gas bubbles were in the old mud bottom.

One thing that arrests attention in such a place is the abruptness of the change from one species of rock to another, as marked and sudden as a change in a piece of masonry from brick to stone, or from stone to iron. The two meet but do not mingle. Nature seems suddenly to have turned over a new leaf, and to have begun a new chapter in her great stone book. What happened? There is no evidence in this region of crustal disturbance since the original plateau out of which the mountains were carved was first lifted up in Palaeozoic times, when the earth was in her teens. The indications are that on some quiet day the peaceful waters became suddenly charged with new material and the streams or rivers from some unknown land in the vicinity poured it into the old Devonian lakes where it hardened into rock. The changes indicated by these streaks of soft red sandstone suddenly alternating with the hard laminated Catskill formation, well up the mountain-sides, with a sharp dividing line between them, occurred many times during the Devonian Age. During one geologic day the earth-building forces brought one kind of material, and the next day material of quite another kind, and this alternation without any change of character seems to have kept up for millions of years. How curious, how interesting! Both from near-by land surfaces, and yet so different from each other! How difficult to form any mental picture of the condition of things in those remote geologic ages! It is as if one day it had snowed something like brick-dust to a depth of many feet, and the next day it had snowed a dark-gray dust of an entirely different character, and that this alternation of storms had kept up for ages. Long before we reach the tops of the mountains, or at about a thousand feet above the river valley, the red soft strata cease, and the hard dark, cross-bedded gray rock continues to the top.

In the higher peaks of the southern Catskills another kind of rock begins to appear before the summit is reached – a conglomerate. The storm of dark snow has turned to a storm of white hail. As you go up, you seem to be climbing into a shower of quartz pebbles. Presently you begin to see here and there a pebble embedded in the rocks; then, as you go on, you see more of them, and still more; it is like the first sprinkle of rain that precedes the shower, till, long before you reach the summit, the regular downpour begins, the rocks become solid masses of pebbles embedded in a gray hard matrix; there are many hundreds of feet of them. On the top the soil is mainly sand and coarse gravel from the disintegrated rock.

The streams at the foot of the mountains abound in fragments of this pudding-stone or conglomerate, and in the hard, liberated quartz pebbles. These pebbles were rolled on an ancient sea-beach incalculable ages ago, and now they are being rolled and worn again by the limpid waters of the Catskill trout-brooks. What varied fortune the whirligig of time brings to quartz pebbles as well as to men!

Of course the Catskills were under water when this conglomerate was laid down upon them. The coal age was near at hand, and a conglomerate akin to this of the tops of the Catskills underlies the coal measures. The Catskill plateau was lifted up before Carboniferous times began, so that there is no coal in this region. We should have to look overhead for it instead of underfoot. When the Catskill plateau rose above the waters, Pennsylvania and most of the continent to the west was under the sea, receiving additional deposits, thousands of feet thick in many places, and in due time supporting a vegetation that gave us our vast deposits of coal.

The geologic tornado that brought this hailstorm of quartz pebbles, so marked in the conglomerate that caps the highest Catskills, seems to have been a general storm over a large part of the northern hemisphere, as this conglomerate underlies the coal measures, both in this country and in Europe. It must have occurred in late Devonian or early Carboniferous times. On the top of Lookout Mountain, in Tennessee, I gathered a handful of pebbles that had weathered out of the Carboniferous sandstone that the ages have exposed on the summit.

An earlier storm of quartz pebbles occurred in Silurian times, which formed the Oneida conglomerate in central New York, and the Shawangunk range in southern New York. This latter range is a vast windrow made up of small pebbles varying in size from peas to large beans, cemented together by quartz sand. It is several hundred feet thick and runs southwest through Pennsylvania into Virginia, affording another proof of the abundance of quartz rock in those early geologic ages. Dana thinks this conglomerate gives us an idea of the seashore work of that period. Only on a seashore could the crushed material have been sorted and distributed in this way. According to the published views of a natural philosopher on the Pacific Coast, this rain of rock material from the heavens is no myth. He believes that the earth in its early history was surrounded by a series of numerous concentric rings of floating cosmic matter, like the rings of Saturn, and that from time to time these rings collapsed and their material fell to earth helping to make up the vast series of stratified rocks. This theory certainly simplifies some of the problems of the geologist. My Catskills did not have to go down under the sea to get this coat of mail of quartz pebbles, or these alternate layers of red and gray sandstone, and the question of the abrupt ending and beginning of the different series is easily solved; as is also the larger question of where all the diverse material of our enormous system of stratified rock, reckoned by some geologists to be not less than twenty miles thick in North America, came from. In some parts of Scotland, the old red sandstone, according to Geikie, is twenty thousand feet thick. This explanation of the California theorist gives us all this material, and gives it in the original packages. I wish I could believe it true – and be thankful that there are no more rings to collapse!

How one would like to know the history of this conglomerate that caps the higher Catskills! What stone-crusher reduced the quartz rock and sorted the fragments so evenly? The stone-crushing plant that turned out the material for most of the other rocks ground "exceeding fine," but in this instance they turned out a very coarse product, though a very uniform one. On the shores of some Palaeozoic sea have these pebbles been rolled and worn. Only upon one sea-beach have I seen pebbles of this size in lieu of sand, and that was upon Dover beach, on the coast of England. Instead of the hissing of the sands when the breakers come in, there rises the sound of the multitudinous rattling of these myriads of pebbles. Some old Devonian seashore has sent up a like sound where these Catskill pebbles were washed by the waves.

The rock-crushing plants must have been very busy in the early geologic ages, and quartz rock must have been a drug in the market. We see no natural forces at work now reducing rocks to coarse gravel on any scale comparable to that which must have taken place in Silurian times when the Shawangunk rocks and the Oneida conglomerate were laid down. In any case, where were the quartz mountains from which they came, and where were the forces that ground them up? "From lands to the eastward," geologists think, but of such lands there are no traces now.

On the Pacific Coast of southern California I saw a strip of country nearly a hundred miles long and from fifteen to twenty miles wide that was mainly made up of large quartz pebbles. The land was thrown into gentle hills and ridges which became higher as they approached the mountains. Near its inland margin I heard of a search for oil that had been made there, the drill going through nine hundred feet of pebbles and striking the granite rock – an unlikely place for oil. But think of the quartz mountains that must have been broken up and put through the mill of the Pacific to form all the vast banks of water-worn pebbles!

In South America Darwin saw hills and mountains of pure quartz. Not far from Buenos Ayres they formed tablelands or mesas, without cleavage or stratification. On the Falkland Islands he found the hills of quartz and the valleys filled with "streams of stone" – huge fragments of quartz rock varying in size from a few feet in diameter "to ten or even more than twenty times as much." Darwin thinks that these streams of quartz stones may have had their origin in streams of white lava that had flowed from many parts of the mountains into the valleys, and then, when solidified, were rent by some enormous convulsion into myriads of fragments. Some such titanic force of nature must have been the stone-crusher that converted vast hills of quartz into the fragments that make up the Shawangunk Mountains, the Oneida conglomerate, and the conglomerate on the tops of the Catskills.

In our Northern States there are two classes of rocks: the place rocks, and the wanderers, or drift boulders. The boulders are in some ways the more interesting; they have a story to tell which the place rock has not; they have drifted about upon a sea of change, slow and unwilling voyagers from the North many tens of thousands of years ago; now they lie here in the fields and on the hills, shipwrecked mariners, in some cases hundreds of miles from home. But usually they have been plucked from the neighboring ledges or mountains, and shoved or transported to where they now lie. In nearly all cases the sharp points and angles have been rubbed down, as with most travelers, and they lie about the fields like cattle ruminating upon the ground.

"The shadow of a great rock in a weary land" is pretty sure to be the shadow of a drift boulder. The rock about which, and on which, we played as children was doubtless a drift boulder; the rocks beneath which the woodchucks and the foxes burrow are drift boulders; the rock under the spreading maples where the picnickers eat their lunch is a drift boulder; the rock that makes the deep pool in the trout-stream of your boyhood is a drift boulder; the rocks which you helped your father pry up from the fields and haul to their place for the "rock bottom" of the stone wall, in the old days on the farm, were all drift boulders. How sod-bound many of them were, and how the old oxen used to settle into their bows with rigid muscles in pulling them from their beds! If you had looked on their under sides you would have seen how smoothed and worn most of them were. They had been hauled across the land by oxen of another kind long before yours were heard of.

The rocks that give the eyebrows to the faces of the hills are place rocks – the cropping-out of the original strata. The place rock gives the contour to the landscape; it forms the ledges and cliffs; it thrusts a huge rocky fist up through the turf here and there, or it exposes a broad smooth surface where you may see the grooves and scratches of the great ice sheet, tens of thousands of years old. The marks of the old ice-plane upon the rocks weather out very slowly. When they are covered with a few inches of soil they are as distinct as those we saw in Alaska under the edges of the retreating glaciers.

One day, on the crest of a hill above my Lodge on the home farm in the Catskills, I used my spade to remove five or six inches of soil from the upper layer of rock in order to prove to some doubting friends that a page of history was written here that they had never suspected. I quickly disclosed the lines and the grooves, nearly as sharp as if made but yesterday, and as straight as if drawn by a rule, running from northeast to southwest. Across the valley, a third of a mile away, I uncovered other rock surfaces on the same level, that showed a continuation of the same lines. The great jack-plane had been shoved across the valley and over the mountaintops and had taken off rocky shavings of unknown thickness.

The drift boulders are not found beyond the southern limit of the great ice-sheet – an irregular line starting a little south of New York and running westward to the Rocky Mountains, but in southern California I saw huge granite boulders that looked singularly like New England drift boulders. They cover the hill called Rubidoux at Riverside. I overheard a tourist explaining to his companions how the old glaciers had brought them there, apparently ignorant of the fact that they were far beyond the southern limit of the old ice-sheet. It is quite evident that they were harder masses that had weathered out of the place rock and had slowly tumbled about and crept down the hill under the expansive power of the sun's rays. But I saw one drift boulder in southern California that was a puzzle; it was a water-worn mass of metamorphic rock, nearly as high as my head, at the end of a valley, several miles in among the hills, with no kindred rocks or stones near it. It was evidently far from home, but what its means of transportation had been I could only conjecture.

Amid the flock of gray and brown boulders that dot my native fields, there is here and there a black sheep – a rough-coated rock much darker than the rest, which the farmers call firestone, mainly, I suppose, because it does not break or explode in the fire. It is a kind of conglomerate, probably what the geologists call breccia, made up of the consolidated smaller fragments of older crushed rocks. The material of which it is composed is of unequal hardness, so that it weathers very rough, presenting a surface deeply pitted and worm-eaten, which does not offer an inviting seat. These rocks wear a darker coat of moss and lichens than the others and seem like interlopers in the family of field boulders. But they really belong here; they have weathered out of the place strata. Here and there one may find their dark worm-eaten fronts in the outcropping ledges. They were probably formed of the coarser material – a miscellaneous assortment of small thin water-worn fragments of rocks and mud and coarse sand – that accumulated about the mouths of the streams and rivers which flowed into the old Devonian lakes and seas. They are not made up of thin sheets like the other rocks, and seem as if made at a single cast. They are as rough-coated as alligators, and do not, to me, look as friendly as their brother rocks. They stand the fire better than other stone. The huge stone arch in my father's sugar bush, in which the great iron kettles were hung, was largely built of these stones. I think the early settlers used them to line the open fireplaces in their stone chimneys. Along the Hudson they used slate, which is also nearly fireproof.

I know a huge iron-stone rock lying at the foot of a hill, from beneath which issues one of the coldest and sweetest springs in the neighborhood. How the haymakers love to go there to drink, and the grazing cattle also! Of course, the relation of the rock to the spring is accidental. The rocks help make the history of the fields, especially the natural history. The woodchucks burrow beneath them, and trees and plants take root beside them. The delightful pools they often form in a trout-stream every angler remembers. Their immobility makes the mobile water dissolve and excavate the soil around and beneath them, and afford lairs for the big trout. I know of a large one that stood on the edge of the road where it snubbed the wagon-wheels as they came along. For generations it had defied the road-menders, till one June day a farmer of more pluck and endurance than usual tackled it with a heavy crowbar, and, after a prolonged effort, split off a huge slab from its top, making it, as the path-master said, "haul in its horns." When a boy I saw my elder brother drill a hole in one with a churn drill, and with a charge of powder blast it into four pieces, which were used in the foundation of a wall by the roadside. As I pass along that road now, after sixty-five years, I see the square faces of that rock with a section of the drill-hole on the corner of each, and think of my brother. It was before the time of fuses, and I remember he primed the blast by the spindle method, and then laid a train of powder with a fragment of paper at the end of it. A lighted match was touched to the paper, and then we ran to a safe distance as fast as our legs could carry us.

How geologic time looks out from the ledges and walls of gray rocks unmindful of us human ephemera that pass! It has seen the mountains decay and the hills grow old. The huge drift boulders rest on the margin of meadows and fields, or stand sentry to the woods, and though races and kingdoms pass, scarcely the change of a wrinkle disturbs their calm stone faces. Yet time gets the better of them also. The frowning ledge melts as inevitably as a snowbank.

Geologic time is the most potent of the gods of change. He wields an invisible hammer beside which the hammer of Thor is a child's toy. Its slow, silent blows break in through granite rocks as big as a house. The traveler sees them along the road when he enters Yosemite; he may see them in New England; he may see them on Lake Mohonk, or on the Shawangunk Mountains in New York – sheer cleavage of rock-masses from fifty to one hundred feet through – a clean break while the huge fragment of the mountain is lying where it fell. It is as if the sunbeams or star-beams did it, as if the snows of winter and the dews of summer had the force of dynamite.

When I get especially rock-hungry, and the troglodyte in me gets restless, as he is apt to in all of us, I take a walk to the ledges on Pine Hill, or on Hemlock Ridge, and prowl about their caverns and loiter under their overhanging strata, putting my hand in the little niches and pockets where I kept my trinkets and choice possessions when I was a troglodyte, inspecting the phœbe's mossy nest on a little shelf where the four-footed beasts cannot reach it, cleaning out the spring that shows like a small eye under the rocky eyebrow, creeping through what we boys called the "Indian oven."

When you want to read a stirring and heroic chapter in the great rock volume of the earth, the very Iliad or Odyssey of the rocks, go to the Grand Canon of the Colorado, or to Yosemite. As you gaze, a sentence from Job may come to your mind as it did to a friend of mine – "Where wast thou when I laid the foundations of the earth?"

All through the Southwest the great book of geologic Revelation lies open to the traveler in an astonishing manner. Its massive but torn and crumpled leaves of limestone, sandstone, and basalt lie spread out before him all through Colorado, New Mexico, and Arizona, and he may read snatches of the long geologic record from the flying train.

I myself need not go so far to see what time can do with the rocks. On the Shawangunk range of mountains in my own State are scenes that suggest a rocky Apocalypse. It is as if the trumpet of the last day had sounded here in some past geologic time. The vast rock-strata of coarse conglomerate, hundreds of feet thick, has trembled and separated into huge blocks, often showing a straight, smooth cleavage like the side of a cathedral. As a matter of fact, I suppose there was no voice of the thunder or of earthquake that wrought this ruin, but the still small voice of heat and cold and rain and snow. There is no wild turmoil or look of decrepitude, but a look of repose and tranquillity. The enormous four-square fragments of the mountain stand a few feet apart, as if carefully quarried for a tower to reach the skies. In classic simplicity and strength, in harmony and majesty of outline, in dignity and serenity of aspect, I do not know their equal. They are truly Greek in their composure and restraint – impressive, like a tragedy of Æschylus, in their naked grandeur. No confusion of tumbled and piled fragments, no sublimity of wreckage and disorder, but the beauty of simplicity, the impressiveness of power in repose.

What a diverse family is this of the stratified rocks! Never did the members of the human family – Caucasian, Negro, Jew, Japanese, Indian, Eskimo, Mongolian – differ more from one another than do the successive geological formations. White and black, hard and soft, coarse and fine, red and gray, yet all in the same line of descent – all dating back to the same old Adam rock of the Azoic period. Time and circumstance, conditions of water and air, of sea and land, seem to have made the difference. As the races of men were modified and stamped by their environment, so the diverse family of rocks reflects the influence of both local and general conditions. When analyzed, their constituents do not differ so much. As in the different races of men we find the same old flesh and blood and bones, so in the rocks we find the same quartz sand and compounds of lime and iron and potash and magnesia and feldspar, yet in quantity and character what a world of difference! How differently they are bedded, how differently they weather, how differently they submit to the hammer and chisel of the mason and the stonecutter! Some rocks seem feminine, smooth, fine-grained, fragile, the product of deep, still water; others are more masculine, coarse, tough, the product of waters more or less turbid or shallow.

The purity of the strain of the different breeds of rocks is remarkable; about as little crossing or mingling among the different systems as there is among the different species of animals: considering the blind warring and chaos of the elements out of which they came, one can but wonder at the homogeneity of the different kinds. They are usually as uniform as if their production had been carefully watched over by some expert in the business, – which is, indeed, the case. This expert is water. Was there ever such a sorter and sifter? See the vast clay-banks, as uniform in quality and texture as a snow-bank, slowly built up in the privacy of deep, still rivers or lakes during hundreds or thousands of years, implying a kind of secrecy and seclusion of nature. Mountains of granite have been ground down or disintegrated, and the clay washed out and carried in suspension by the currents, till it was impounded in some lake or basin, and then slowly dropped. The great clay-banks and sand-banks of the Hudson River Valley doubtless date from the primary rocks of the Adirondack region. Much of the quartz sand is still in the soil of that region, and much of it is piled up along the river-banks, but most of the clay has gone downstream and been finally deposited in the great river terraces that are now being uncovered and worked by the brickmakers. The sand and the clay rarely get mixed; the great hydraulic machine turns out a pretty pure product. The occasional mingling of sand and gravel shows that at times the workmen nodded, but the wonder is that, on the whole, the two should be so thoroughly separated, and so carefully deposited, each by itself. Flowing water drops its coarser material first, the sand next, and the mud and silt last. Hence the coarser-grained rocks and conglomerates are built up in shallow water near shore, the sandstones in deeper water, and the slates and argillaceous rocks in deeper still. The limestone rocks, which are of animal origin, also imply deep, calm seas during periods that embrace hundreds and thousands of centuries. It is, then, the long ages of peace and tranquillity in the processes of the earth-building forces that have contributed to the homogeneity of the different systems of secondary rocks. What peace must have brooded over that great inland sea when those vast beds of Indiana limestone and sandstone were being laid down! A depth of thousands of feet of each without a flaw. Vast stretches of Cambrian and Silurian and Devonian time were apparently as free from violent movements and warrings of the elements as in our own day.

Occasionally in a system of rocks one may see a change of color over a considerable area, as from gray or brown to red, with small fragments of older and redder rocks embedded in them. I fancy such streaks were caused by a sudden flood or freshet that carried new material worn from a distant land-surface into the sea or into the impounded waters.

It would seem to require as distinctly an evolutionary process to derive our sedimentary rocks from the original igneous rocks as to derive the vertebrate from the invertebrate, or the mammal from the reptile. Of course, it could not be done by a mechanical process alone. It has been largely a chemical process and, no doubt, to a certain extent, a vital process also. The making of a loaf of bread is, up to a certain point, a mechanical process; then higher and finer processes set in. And all the cake and pastry and loaves in the bakeshop do not differ from the original bin of wheat any more than the great family of secondary rocks differs from the unmilled harvest of the earth's original crust. And the increase in bulk seems to have been quite as great as that which the bin of wheat undergoes in passing from the kernel to the loaf or the roll. The leaven that went to the making of our shale and sandstone loaves seems to have been contributed by the sea when the batch was mixed and baked. Little doubt that the bulk of the material of the sedimentary rocks came through the process of erosion and deposition from the original igneous rocks, but how has it expanded and augmented during the process! It seems to have swelled almost as the inorganic swells in passing into the organic.